function ajax(opt) {
  opt = opt || {};
  opt.method = opt.method.toUpperCase() || 'POST';
  opt.url = opt.url || '';
  opt.async = opt.async || true;
  opt.data = opt.data || null;
  opt.success = opt.success || function () {};
  opt.withCredentials = opt.withCredentials || false;
  var xmlHttp = null;
  if (XMLHttpRequest) {
    xmlHttp = new XMLHttpRequest();
  } else {
    xmlHttp = new ActiveXObject('Microsoft.XMLHTTP');
  }
  var params = [];
  for (var key in opt.data) {
    params.push(key + '=' + opt.data[key]);
  }
  var postData = params.join('&');
  if (opt.method.toUpperCase() === 'POST') {
    xmlHttp.open(opt.method, opt.url, opt.async);
    xmlHttp.withCredentials = opt.withCredentials;
    // xmlHttp.setRequestHeader('Content-Type', 'application/x-www-form-urlencoded;charset=utf-8');
    // xmlHttp.setRequestHeader('Content-Type', 'application/x-www-form-urlencoded');
    xmlHttp.send(opt.data);
  } else if (opt.method.toUpperCase() === 'GET') {
    xmlHttp.open(opt.method, opt.url + '?' + postData, opt.async);
    xmlHttp.withCredentials = opt.withCredentials;
    xmlHttp.send(null);
  }
  xmlHttp.onreadystatechange = function () {
    if (xmlHttp.readyState == 4 && xmlHttp.status == 200) {
      const data = JSON.parse(xmlHttp.responseText);
      // 重定向
      if (data.status === 3) {
        window.window.location.href = data.data.url;
      }
      opt.success(data);
    }
  };
}

module.exports = ajax;
